<div>Heavy rare earth elements are essential in renewable energy and high-tech products. Some natural rare earth element (REE) deposits exhibit heavy rare earth element (HREE) enrichment from &lt;&nbsp;10% to ~85% of the REE budget (Williams-Jones et al., 2015). </div><div><br></div><div>Controls on REE fractionation in hydrothermal systems are imposed by (1) changes in the relative stability of REE aqueous complexes with temperature (Migdisov et al., 2016) and (2) incorporation or rejection of REE by crystalline structures. Also, the REEs are invariably found as solid solutions but not as pure minerals. REE and yttrium (Y) sulphate complexes are some of the most stable REE and Y aqueous species in hydrothermal fluids (Migdisov and William-Jones, 2008, 2016; Guan et al., 2022) and may be responsible for REE transport and deposition in sediment-hosted deposits. Within the unconformity-related deposits, REEs are hosted mostly by xenotime ((Y,Dy,Er,Tb,Yb)PO4) and minor florencite ((La,Ce)Al3(PO4)2(OH)6) (Nazari-Dehkordi et al., 2019). Modelling the stability of xenotime in the H-O-Cl-(±F)-S-P aqueous system is critical for understanding HREE enrichment in this mineral system.</div><div><br></div><div>We use a newly derived thermodynamic dataset depos for REESO4+ and REE(SO4)2‑ aqueous complexes to generate stability diagrams illustrating mechanisms of REE transport and deposition in the above deposits. Sulphate REE complexes may dominate even in chloride-rich brines and facilitate REE mobilization in acid oxidizing environments. Previously Nazari-Dehkordi et al. (2019) proposed an ore genesis model involving the mixing of discrete hydrothermal fluids that separately carried REE + yttrium and phosphorus. The speciation model that includes sulphate complexes expands this scenario; a process resulting in fluid neutralization or reduction will also promote precipitation of xenotime enriched in HREEs.&nbsp;</div><div><br></div>This Abstract was submitted/presented to the 2022 Specialist Group in Geochemistry, Mineralogy and Petrology (SGGMP) Conference 7-11 November (https://gsasggmp.wixsite.com/home/biennial-conference-2021)

The Bureau of Mineral Resources, Geology and Geophysics (BMR) has developed a model for the distribution of gold, platinum, palladium and uranium at Coronation Hill. There is strong evidence that deposits of this type may occur at other places within the Conservation Zone. This report presents the results of systematic field investigations carried out by the BMR for the Resource Assessment Commission inquiry into the Resources of the Kakadu Conservation Zone. The brief was to "conduct and interpret geological, geochemical, and geophysical surveys as required to provide the best possible basis, within the limited time available, for estimating the resource potential elsewhere in the Conservation Zone" (ie. excluding the defined resource at Coronation Hill). During June/July 1990, regional stream sediment geochemical surveys were undertaken and limited soil sampling was done. Detailed geochemical rock chip sampling was also carried out at the old mines, prospects and occurrences and a review was made of company work undertaken at these localities. From these surveys a relative evaluation of the likelihood for mineralisation (i.e.. prospectivity) of each anomaly and/or prospect is made. An quantitative estimate of the undiscovered resource of the region is the topic of a separate BMR report. The Kakadu Conservation Zone was the site of intense regional uranium exploration from about 1954 to 1964 and again from 1968 to 1976. There are numerous signs of mining activity including seven open pits and 5000m of underground workings. At most of the prospects there is a network of access roads, benches and costeans. The Conservation Zone has never been systematically or rigorously tested for minerals other than uranium. Except for the recent work at Coronation Hill, exploration for gold consisted only of analysing those drill cuttings in the uranium drilling programs that had visible gold. The Conservation Zone contains many areas with geological fault structures, rock types and rock alteration favourable to the occurrence of further gold+palladium+platinum (± uranium) mineralization of the Coronation Hill type. Other localities contain high levels of rare earth elements, representing the potential for styles of mineralisation other than precious metals. Economically significant gold, palladium and platinum assay results were obtained in stream sediment and soil surveys. High gold values from 14 stream sediment sites are comparable to assay results adjacent to some demonstrated economic resources of gold elsewhere in Australia. Some of these zones occur in areas not previously known to have mineralisation. The majority of the prospects and mines in the Conservation Zone were located as a result of geophysical surveys using either radiometric or self potential surveys. A review of the geophysical data shows that there are many untested airborne radiometric anomalies and self potential anomalies which are potentially related to mineralisation. Systematic variations in mineralisation styles and structural settings, rock alteration characteristics and rock types indicate that all the mineralisation styles are probably related to one major mineralisation system. An empirically based new ore genesis model is presented which integrates these variations and which is used as a predictive tool in assessing the potential mineralisation within the Conservation Zone. The model relates gold and palladium/platinum to feldspar-bearing rocks; uranium is usually only found where carbon-rich shales or chloritic rocks are present. Where there is quartz veining present gold is associated with minor amounts of arsenic, copper and/or uranium. These deposit types are surrounded by altered rocks that are depleted in sodium, calcium, silica and thorium. These same elements have been moved to higher levels, and therefore rocks enriched in these elements are considered as possible indicators of gold, platinum, palladium and uranium mineralisation at depth. Zones of quartz veining at these higher levels are potential sites for gold and minor uranium mineralisation. At even higher levels, zones of thorium enrichment are related to high concentrations of rare earth elements, which offer secondary but significant economic targets. Therefore the possibility exists for a tiered arrangement of differing types of mineral deposits. Gold may also be associated with iron stones similar to the Tennant Creek deposits, offering yet another deposit style for consideration in any resource assessment analysis. The mineralisation is located in positions where openings in the rocks have been created by differential movement along fault zones. Two types of openings control most of the Conservation Zone mineralisation. Near-horizontal tabular ore zones are related to openings created along unconformities (major breaks in the geological rock record). Steep cigar-shaped ore zones are formed in openings created at bends in near-vertical fault lines. Past exploration (including drilling) is evaluated to determine how well these geometries have been tested. Coronation Hill is an intensively faulted zone in which many rock types are juxtaposed. Mineralisation consists of gold, palladium and platinum, with both uranium-poor and uranium-rich zones. Most of the uranium-rich zones are outside of the proposed open pit. The deposit is open at depth and the structural setting and mix of rock types suggest that extensions of mineralisation will occur at depth. Repetitions of the Coronation Hill style of mineralisation are likely at Coronation Hill West, where the geology is a direct mirror-image of the Coronation Hill deposit. Gold mineralisation at El Sherana is high grade but discontinuous. It occurs in spatial association with, but often slightly removed from, uranium mineralisation. Both occur in shallow northwest-pitching cigar-shaped bodies which do not appear to persist at depth owing to this geometry. The recent five hole drilling program by the Coronation Hill Joint Venture Partners failed to test the distribution of mineralisation, and the area still has a very high potential. El Sherana is a small part of a highly prospective area that extends for over three kilometres from Stag Creek through to High Road and beyond. The Palette area is structurally and stratigraphically complex, and is so far largely untested for gold, palladium and platinum. Four drill holes by the Coronation Hill Joint Venture Partners tested a Coronation Hill-like structural target but obtained no significant results. More work is needed to properly test the potential of the many possibly mineralised structural sites of this area, which extends along strike for at least two kilometres from Cliff Face to Skull 2. Other old prospects which warrant further exploration for gold, platinum and palladium include the Airstrip region, the Monolith-Koolpin Creek area, Scinto 5 North, the Saddle Ridge area and the Clear Springs Fault Group between Scinto 5 and Scinto Camp. Areas indicated as moderately to highly prospective by this study which have not previously been intensively prospected include Saddle Ridge Northeast, Pul Pul Hill, Gimbat Ridge, and along the Fisher Fault. The history of uranium development in this region is of small, pod-like high grade deposits. This study suggests that such pods are controlled by the intersection of near-vertical trending carbonaceous or chlorite-rich basement rocks and subvertical faults. Additional uranium deposits are likely to be found. The unusual style of platinum and palladium mineralisation is dependent upon several distinctive geological parameters. As these are rarely coincident elsewhere in Australia there is a low probability of locating other deposits of this style in other regions. This is endorsed by the failure of intensive exploration in the last five years to locate a new economic resource of these metals in Australia. Of the 50 sites described in this report several are rated as highly prospective. A comparison with exploration case histories in other regions of Australia suggests that the presence of significant economic resources additional to Coronation Hill is very likely. Any future exploration would be assisted by the extensive existing network of about 300 km of roads, including access to the top of the Scinto Plateau, and numerous trenches, benches and adits. Most of the roads are in reasonable condition and would require minimal bulldozing to repair them.

<div>The push of mineral exploration under cover requires developing new geochemical exploration approaches. Detailed hydrogeochemistry addresses these needs and is valuable as a non-invasive mineral exploration technique that can identify lithological changes and dispersion signatures associated with mineralisation. Here we integrate whole-rock geochemistry and hydrogeochemistry to evaluate suitable geochemical tracers in groundwater for detecting phosphate and/or Pb-Zn style mineralisation in the Georgina Basin. The known Georgina Basin’s phosphate deposits are within the basin’s aquifers, providing groundwater near deposits greater exposure and opportunity for water-rock interactions with mineralised geology, resulting in trace element and isotope signatures of mineralisation at detectable levels. These tracers can then be applied elsewhere in the basin as a screening tool for detecting mineralisation. To achieve this, we collected rock geochemistry from the MinEx CRC East Tennant National Drilling Initiative Campaign (ME-ET) drillcore, and integrated it with nearby hydrogeochemistry (from the Northern Australia Hydrogeochemical Survey (NAHS)). </div><div><br></div><div>The NAHS was collected by Geoscience Australia as part of EFTF, which included 170 samples from Georgina Basin aquifers. This hydrogeochemistry dataset is high quality, due to robust sampling, QA/QC procedures and a comprehensive analysis suite, making it a useful tool for mineral exploration in the Georgina Basin. The ME-ET drilled 10 stratigraphic holes east of Tennant Creek, Northern Territory, in support of Geoscience Australia’s Exploring for the Future program (EFTF). Seventy six Georgina Basin rock samples were collected for whole rock geochemistry and a subset for Pb and Sr isotopes. Samples were selected to target: 1) background unmineralised lithostratigraphy, 2) intervals with groundwater intersections, and 3) transects through zones with anomalous concentrations of P, Pb, Zn and Cu, as identified by portable XRF analysis. </div><div><br></div><div>Initial exploratory data analysis of the hydrogeochemistry is conducted at various scales using principle component analysis and clustering approaches to identify the key attributes (major and trace elements, isotopes, hydrogeology etc.) that are associated with higher P content in the groundwater. These relationships are tested by comparing groundwater samples proximal (in depth and spatially) to high P compositions in the host rock, providing insight into the water-rock interactions taking place. Additionally, vertical whole rock geochemistry transects within the drill-holes are investigated to evaluate the trace element and/or isotopic features that are diagnostic of the enriched phosphate zones. We take the robust geochemical relationships identified from both approaches and apply them as tracers across the NAHS to flag areas of potential undiscovered mineralisation. As we will demonstrate, the NAHS can detect subtle or diluted mineralisation signatures, and underpins a revised understanding of phosphate mineral prospectivity in the Georgina Basin.</div> Abstract submitted and presented at 2023 Australian Earth Science Convention (AESC), Perth WA (https://2023.aegc.com.au/)

This Record details rhenium–osmium (Re–Os) dating of molybdenite separated from quartz veins associated with tungsten mineralisation at the Hit or Miss deposit of the Hatches Creek tungsten field, Warramunga Province. Two samples of molybdenite were collected from the former mine: sample FR17MVM001 as drill chips from a tungsten-mineralised quartz vein in drillhole HCRC021, and sample FR17MVM002 from a quartz vein in surface workings associated with tungsten and molybdenum. Molybdenite was dated to determine an absolute age for tungsten mineralisation at the deposit. The Re–Os molybdenite model ages obtained were 1677 ± 10 Ma and 1602 ± 9 Ma respectively. These ages are tentatively interpreted as mineralisation and/or remobilisation ages for molybdenum and tungsten, and the associated bismuth and copper at the Hit or Miss deposit; they also provide timing constraints on mineralisation in the wider Hatches Creek tungsten field. Low Re concentrations in the samples (1–2 ppm) are consistent with an evolved crustal source for the tungsten mineralisation. The older of the two Re–Os model ages is broadly consistent with previous age determinations for tungsten mineralisation and felsic intrusions in the Warramunga Province using Ar–Ar muscovite and U–Pb zircon dating methods. Although the geological significance of the new Re–Os molybdenite age is uncertain, the results are tentatively interpreted to record a protracted episode of tungsten, copper and molybdenum mineralisation in the Warramunga Province between ca 1700 –1600 Ma, associated with evolved felsic intrusions. <b>BIBLIOGRAPHIC REFERENCE: </b>McGloin MV, , Huston DH and Norman M, 2019. Summary of results. Re–Os molybdenite dating of the Hit or Miss deposit, Hatches Creek tungsten field, Warramunga Province. <i>Northern Territory Geological Survey</i>, Record 2019-010.

<div>This short video of approximately 5 minutes illustrates the timing of magmatism and mineralisation across Australia, from 3.5 billion years ago to the present. The video is based on a compilation of geochronology data delivered via the GA Portal in the Geochronology and Isotopes persona, and the compilation of mineral deposits of Huston et al. (2021).</div>

The Paleo- to Mesoproterozoic McArthur Basin and Mount Isa region of northern Australia (Figure 1) is richly-endowed with a range of deposit types (e.g., Ahmad et al., 2013; Geological Survey of Queensland, 2011). These include the basin-hosted base metal (Zn-Pb-Ag) deposits of the North Australian Zinc Belt, the richest zinc province in the world (Geological Survey of Queensland, 2011; Huston et al., 2006), as well as Cu (e.g., Mt Isa Copper) and IOCG (e.g., Ernest Henry) deposits (Geological Survey of Queensland, 2011). The giant size of the base metal deposits makes them attractive exploration targets and significant effort has been undertaken in understanding their genesis and setting and developing methodologies and data sets to aid in further discovery. As part of its Exploring for the Future program, Geoscience Australia is acquiring new, and reprocessing old, data sets to provide industry with new exploration tools for these basin-hosted Zn-Pb and Cu deposits, as well as iron-oxide copper-gold deposits. We have adopted a mineral systems approach (e.g., Huston et al., 2016) focussing on regional aspects such as source rocks, locations of mineral deposits, mineralisation haloes and footprints. Increased understanding of these aspects requires knowledge of the background variability of unaltered rocks within the basin. To assist in this we have undertaken a campaign of baseline geochemical studies, with over 800 new samples collected from sedimentary and igneous units of selected parts of the greater McArthur Basin–Mount Isa region. This has allowed us to document temporal and regional background geochemical (and mineralogical) variation within, and between sedimentary and igneous units. The main focus of this work was directed towards aspects of base metal mineralisation; a concurrent GA study (e.g., Jarrett et al., 2019) looking at aspects of hydrocarbon potential was undertaken in parallel. Appeared in Annual Geoscience Exploration Seminar (AGES) Proceedings, Alice Springs, Northern Territory 24-25 March 2020, p. 105

This Record presents new Sensitive High Resolution Ion Micro Probe (SHRIMP) U–Pb geochronological results for five drill core samples from the Rover mineral field, an area of prospective Palaeoproterozoic rocks southwest of Tennant Creek that is entirely concealed below younger sedimentary cover rocks. The work is part of an ongoing collaborative effort between Geoscience Australia (GA) and the Northern Territory Geological Survey (NTGS) that aims to develop better understanding of the geological evolution and mineral potential of this region. It is being undertaken as part of the Northern Territory Government’s Resourcing the Territory (RTT) initiative and the Federal Government’s Exploring for the Future (EFTF) program and was carried out under the auspices of the National Collaborative Framework (NCF) between GA and NTGS. The rocks studied were sampled from drill cores acquired under the Northern Territory Government’s Geophysics and Drilling Collaborations program; the drillholes sampled comprise RVDD0002 (Wetherley and Elliston 2019), MXCURD002 (Burke 2015) and R27ARD18 (Anderson 2010). <b>Bibliographic Reference:</b> Cross A, Huston D and Farias P, 2021. Summary of results. Joint NTGS–GA geochronology project: Rover mineral field, Warramunga Province, January–June 2020. <i>Northern Territory Geological Survey</i>, <b>Record 2021-003</b>.

The footprint of a mineral system is potentially detectable at a variety of scales, from ore deposits to the Earth’s crust and lithosphere. To map these systems, Geoscience Australia has undertaken a series of integrated studies to identify key regions of mineral potential using new data from the Exploring for the Future program, together with legacy datasets. The conductivity anomaly mapped from long-period magnetotellurics (AusLAMP) data with a half-degree resolution has highlighted a structural corridor to the east of Tennant Creek, representing a potential source region for iron oxide copper–gold mineral systems. To refine the geometry of this anomaly, we used a higher-resolution magnetotellurics survey to investigate if the deep conductivity anomaly is linked to the near surface by crustal-scale fluid pathways. The 3D conductivity model revealed two prominent conductors in the resistive host, whose combined responses result in the lithospheric-scale conductivity anomaly mapped in the AusLAMP model. The resistivity contrasts coincide with major structures preliminarily interpreted from seismic reflection and potential field data. Most importantly, the conductive structures extend from the lower crust to the near surface. This observation strongly suggests that the major faults in this region are deep-penetrating structures that potentially acted as pathways for transporting metalliferous fluids to the upper crust where they could form mineral deposits. This result indicates high mineral prospectivity for iron oxide copper–gold deposits in the vicinity of these major faults. This study demonstrates that integration of geophysical data from multiscale surveys is an effective approach to scale reduction during mineral exploration in covered terranes with limited geological knowledge. <b>Citation:</b> Jiang, W., Duan, J., Schofield, A. and Clark, A., 2020. Mapping crustal structures through scale reduction magnetotelluric survey in the East Tennant region, northern Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.